The present invention relates to an improvement in anti-icing systems for aircraft jet engine propulsion systems.
The formation of ice on exposed surfaces of aircraft, such as aircraft wings, propellers, and air inlets of engines has been a problem since the earliest days of heavier-than-air flight. Any accumulated ice adds considerable weight, and changes the airfoil or inlet profile, making the aircraft much more difficult to fly and in some cases causing loss of aircraft. In the case of jet aircraft, large pieces of ice breaking loose from the leading edge of an engine inlet housing can damage rotating blades or other internal engine components and cause engine failure.
One of the most common anti-icing techniques has been the ducting of hot gases into a housing adjacent to the likely icing area. Current techniques to solve this problem generally fall into one of two types of systems: impingement style ring systems or swirl nozzle systems. In each case, the hot gas conduits simply introduce hot gases into a housing, such as the leading edge of a jet engine inlet or a wing leading edge. While these systems are generally effective, their efficiency is degraded by the fact that more thermal energy than needed is introduced in localized regions rather than being more efficiently distributed over the domain of interest. A consequence of these localized “hot” spots is an unfavorable impact on the structural integrity of the housing.
In impingement-style ring systems, hot air is impinged on a metal skin forming an engine inlet lip by strategically positioned holes in an annulus shaped tube that runs 360 degrees around the front of the inlet. The air impinges on the internal surface of the metal skin forming the inlet lip, causing the metal temperature to increase and prevent ice accretion.
Existing swirl nozzles discharge the hot air through multiple holes contained within a single housing, and the result is the formation of a hot air jet flow field. The air is discharged at a high velocity so that it creates a swirling effect in the forward most inlet compartment, commonly referred to as the D-duct lip. The air continues to move 360 degrees around the annular D-duct compartment. It circulates around the compartment several times until it exits into the ambient air through an exhaust port. This circulating and/or swirling hot air heats the inlet lip skin and prevents the accretion of ice, thus mitigating the concern for ice shedding off the lip and impinging on rotating engine blades downstream. Although the figures and verbiage of the specification use nose cowl anti-icing for explanatory purposes, the invention disclosed herein may apply to any other housings subject to ice formation, including but not limited to, wing conduits and ducts.
Both existing systems have limitations. The impingement ring style anti-ice systems have a cumbersome tube and support structure that runs 360 degrees around the front inlet compartment. While these systems generally have very high heat transfer ratios, they also add considerable weight to the propulsion system of the aircraft. Swirl nozzle systems are generally significantly lighter than impingement ring style systems and use less air to anti-ice the lip surface. Both systems impart localized jet impingement which can promote structural degradation and suboptimal efficiency.